1. Field of the Invention
This invention relates to a process for producing polymers of xcex1-olefins, e.g., 1-hexene, 1-octene, 1-decene, 1-dodecene, and the like, comprising a minor amount of a bulky olefinic comonomer, e.g., norbornylene, vinyl cyclohexane, and the like, in the presence of a metallocene catalyst. The invention also relates to the resulting polymers and to lubricant compositions in which the polymer functions as a viscosity modifier.
2. Description of the Related Art
Catalytic oligomerization of olefins is a known technique for manufacturing hydrocarbon basestocks useful as lubricants. Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have been the subject of important research and development in the petroleum industry for several decades, leading to recent commercial production of a number of superior poly(xcex1-olefin) synthetic lubricants (hereinafter referred to as xe2x80x9cPAOxe2x80x9d). These materials are primarily based on the oligomerization of xcex1-olefins, such as C2-C20 olefins. Industrial research effort on synthetic lubricants has generally focused on fluids exhibiting useful viscosities over a wide range of temperature, i.e., improved viscosity index (VI), while also showing lubricity, thermal, and oxidative stability and pour point equal to or better than mineral oil. These newer synthetic lubricants provide lower friction and hence increase mechanical efficiency across the full spectrum of mechanical loads and do so over a wider range of operating conditions than mineral oil lubricants.
Well known structural and physical property relationships for high polymers as contained in the various disciplines of polymer chemistry have pointed the way to xcex1-olefins as a fruitful field of investigation for the synthesis of oligomers with the structure thought to be needed to confer improved lubricant properties thereon. Owing largely to studies on the polymerization of propene and vinyl monomers, the mechanism of the polymerization of xcex1-olefins and the effect of that mechanism on polymer structure is reasonably well understood, providing a strong resource for targeting on potentially useful oligomerization methods and oligomer structures. Building on that resource, oligomers of xcex1-olefins from 2 to 20 carbon atoms have been prepared with commercially useful synthetic lubricants from, e.g., 1-decene oligomerization.
A significant problem in the manufacture of synthetic lubricants is the production of lubricants in a preferred viscosity range in good yield without excessive catalyst deactivation. Frequently, it is difficult to directly produce lower viscosity range lubes without incurring lower yields due to the production of non-lubricant range materials. Methods to control molecular weight of lubricants in the oligomerization step are sought after in the art to overcome the problems in the manufacture of, particularly, lower viscosity lubricants.
Janiak, C. et al., Journal of Molecular Catalysis A: Chemical, 166:193-201 (2001) provide a full literature and patent account of work describing the vinyl polymerization to homo-polynorbornene. The interest in vinyl homo-polynorbornene is driven by its dielectric and mechanical properties for the technical application as an interlevel dielectric in microelectronics applications. The norbornene/olefin copolymerization is covered to some extent for comparison the metal catalysts are presented and important polymer product properties are emphasized.
U.S. patent application Ser. No. 09/637,791, filed Aug. 11, 2000 now abandoned, discloses a liquid polyalphaolefin homo- or copolymer, preferably 1-decene, which is substantially amorphous and obtained by a polymerization process employing hydrogen and a particular type of metallocene catalyst. Additionally, a liquid polyalphaolefin homo- or copolymer containing from 2 to about 12 carbon atoms possess a unique combination of properties, i.e., low molecular weight (Mw), low polydispersity index (Mw/Mn), controllable kinematic viscosity (Kv100), low Iodine Number (I2) and low glass transition temperature (Tg) and are substantially amorphous. These liquid polyalphaolefin homo- or copolymers are useful for manufacturing a variety of products including lubricating oils in which the polyalphaolefin functions as a viscosity modifier.
The present invention is directed to a process for polymerizing xcex1-olefins, such as (but not limited to) 1-hexene, 1-octene, 1-decene, and 1-dodecene, to form low molecular weight oligomers and polymers having viscosities suitable for synthetic lubricant applications wherein the process does not require the use of a secondary hydrogenation step to achieve a saturated polymer. The polymerization is carried out in the presence of minor amounts of a bulky olefinic comonomer, such as norbornene (preferred), vinyl cyclohexane, and the like, so that viscosities as low as 20 cSt can be achieved while containing levels of unsaturation (as measured by iodine number determination) at the limits of the test method.
The monomers are polymerized in the presence of a Kaminsky-type xe2x80x9cmetallocenexe2x80x9d catalyst, which provides for stereochemical control during polymerization. Examples of suitable catalysts include, but not limited to, rac-Et(Ind)2ZrCl2, rac-Et(IndH4)2ZrCl2, rac-Me2Si(Ind)2ZrCl2, rac-Me2Si(IndH4)2ZrCl2, Me2Si(Cp-9-Flu)ZrCl2, Me2C(Cp-9-Flu)ZrCl2, and especially (C6H5)2C(Cp-9-Flu)ZrCl2. These catalysts are commonly used in the polymerization of alphaolefins in conjunction with an alkylaluminum activator, such as methylaluminoxane (MAO), and, possibly, an organoboron activator.
The poly(xcex1-olefin) (PAO) obtained possesses excellent clarity, substantially improved viscosity index, and low temperature properties. By inclusion of both a bulky olefinic comonomer and hydrogen into the polymerization, unsaturation levels are further improved over the inclusion of hydrogen alone in metallocene polymerization, and the need for subsequent hydrogenation of the PAO to remove unsaturation is virtually eliminated.
The PAO formed by this process affords an iodine number of 3 or less for the viscosity range of 40-100 cSt, which is currently commercially available via a different process that involves hydrogenation. This represents both a saving of time and a reduction in production costs from the established production of commercial PAO.
More particularly, the present invention is directed to a process for the preparation of a poly(xcex1-olefin) copolymer comprising polymerizing at least one xcex1-olefin and at least one bulky olefin in the presence of hydrogen and a catalytically effective amount of catalyst comprising the product obtained by combining a metallocene procatalyst with a cocatalyst, the metallocene procatalyst being at least one compound of general formula:
(Cp1R1m)R3(Cp2R2p)MXq
wherein Cp1 of ligand (Cp1R1m) and Cp2 of ligand (Cp2R2p) are the same or different cyclopentadienyl rings, R1 and R2 each is, independently, hydrogen or a hydrocarbyl, halocarbyl, heterocarbyl, hydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, m is 0 to 5, p is 0 to 5 and two R1 and/or R2 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated therewith can be joined together to form a ring containing from 4 to about 20 carbon atoms, R3 is a bridging group bridging Cp1 with Cp2, M is a transition metal having a valence of from 3 to 6, each X is a non-cyclopentadienyl ligand and is, independently, halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, and q is equal to the valence of M minus 2, the cocatalyst being an aluminoxane and it being provided that ligand (Cp1R1m) is different than ligand (Cp2R2p) and bridging group R3 contains at least two bulky groups.
In another aspect, the present invention is directed to a poly(xcex1-olefin) copolymer obtained from the polymerization of at least one xcex1-olefin having from 2 to about 20 carbon atoms and at least one bulky olefin, the process comprising polymerizing the monomers in the presence of hydrogen and a catalytically effective amount of a catalyst comprising the product obtained by combining a metallocene procatalyst with a cocatalyst, the metallocene procatalyst being at least one compound of general formula:
(Cp1R1m)R3(Cp2R2p)MXq
wherein Cp1 of ligand (Cp1R1m) and Cp2 of ligand (Cp2R2p) are the same or different cyclopentadienyl rings, R1 and R2 each is, independently, hydrogen or a hydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, m is 0 to 5, p is 0 to 5 and two R1 and/or R2 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated therewith can be joined together to form a ring fused to the cyclopentadienyl ring, the fused ring containing from 4 to about 20 carbon atoms, R3 is a bridging group bridging Cp1 and Cp2, M is a transition metal having a valence of from 3 to 6, each X is a non-cyclopentadienyl ligand and is, independently, halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, q is equal to the valence of M minus 2, the cocatalyst being an aluminoxane and it being provided that ligand (Cp1R1m) is different from ligand (Cp2R2p) and bridging group R3 contains at least two bulky groups.
In still another aspect, the present invention is directed to a lubricant composition comprising a lubricant and a viscosity-modifying amount of a poly(xcex1-olefin) copolymer obtained from the polymerization of at least one xcex1-olefin having from 2 to about 20 carbon atoms and at least one bulky olefin, the process comprising polymerizing the monomers in the presence of hydrogen and a catalytically effective amount of a catalyst comprising the product obtained by combining a metallocene procatalyst with a cocatalyst, the metallocene procatalyst being at least one compound of general formula:
(Cp1R1m)R3(Cp2R2p)MXq
wherein Cp1 of ligand (Cp1R1m) and Cp2 of ligand (Cp2R2p) are the same or different cyclopentadienyl rings, R1 and R2 each is, independently, hydrogen or a hydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, m is 0 to 5, p is 0 to 5 and two R1 and/or R2 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated therewith can be joined together to form a ring fused to the cyclopentadienyl ring, the fused ring containing from 4 to about 20 carbon atoms, R3 is a bridging group bridging Cp1 and Cp2, M is a transition metal having a valence of from 3 to 6, each X is a non-cyclopentadienyl ligand and is, independently, halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, q is equal to the valence of M minus 2, the cocatalyst being an aluminoxane and it being provided that ligand (Cp1R1m) is different from ligand (Cp2R2p) and bridging group R3 contains at least two bulky groups.
In yet another aspect, the present invention is directed to a method for improving the viscosity index of a lubricant composition comprising adding to the composition a viscosity-modifying amount of a poly(xcex1-olefin) copolymer obtained from the polymerization of at least one xcex1-olefin having from 2 to about 20 carbon atoms and at least one bulky olefin, the process comprising polymerizing the monomers in the presence of hydrogen and a catalytically effective amount of a catalyst comprising the product obtained by combining a metallocene procatalyst with a cocatalyst, the metallocene procatalyst being at least one compound of general formula:
(Cp1R1m)R3(Cp2R2p)MXq
wherein Cp1 of ligand (Cp1R1m) and Cp2 of ligand (Cp2R2p) are the same or different cyclopentadienyl rings, R1 and R2 each is, independently, hydrogen or a hydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, m is 0 to 5, p is 0 to 5 and two R1 and/or R2 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated therewith can be joined together to form a ring fused to the cyclopentadienyl ring, the fused ring containing from 4 to about 20 carbon atoms, R3 is a bridging group bridging Cp1 and Cp2, M is a transition metal having a valence of from 3 to 6, each X is a non-cyclopentadienyl ligand and is, independently, halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, q is equal to the valence of M minus 2, the cocatalyst being an aluminoxane and it being provided that ligand (Cp1R1m) is different from ligand (Cp2R2p) and bridging group R3 contains at least two bulky groups.
The poly(xcex1-olefin) polymers of this invention are substantially saturated, i.e., one possessing a low iodine number, which is discussed hereinbelow, and can be obtained by copolymerizing at least one xcex1-olefin monomer, e.g., 1-decene, with at least one bulky olefin, e.g., norbornene, in the presence of a catalyst composition formed by activating a metallocene procatalyst with a suitable cocatalyst. Preferably, hydrogen will also be present in the polymerization.
The xcex1-olefins suitable for use in the preparation of the saturated poly(xcex1-olefin) polymers described herein contain from 2 to about 20 carbon atoms, preferably from about 6 to about 16 carbon atoms. Suitable xcex1-olefins include, but are not limited to, ethylene, propylene, 2-methylpropene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, and the like. Preferred xcex1-olefins for use herein are 1-hexene, 1-octene, 1-decene, and 1-dodecene, with 1-decene being most preferred.
The poly(xcex1-olefin) copolymers of the present invention comprise greater than fifty mole percent of polymerized xcex1-olefin and less than fifty mole percent, but greater than zero mole percent, of the bulky olefinic comonomer. Preferably, the copolymers can contain up to about 99.9, more preferably from about 90 to about 99.7, and most preferably from about 93 to about 99.6, mole percent polymerized xcex1-olefin, e.g., polymerized 1-decene.
The xe2x80x9cbulky olefinxe2x80x9d comonomers that can be used in the practice of the invention are generally norbornenes or cyclo-monolefins that are typically formed by the Diels-Alder reaction of cyclopentadiene and an olefin, e.g., norbornene, 5-methyl-2-norbornene, 5-ethyl-2-norbornene, and the like. The cyclic and polycyclic olefins disclosed in U.S. Pat. No. 5,324,801, hereby incorporated herein by reference in its entirety, can also be used. Specifically, such cyclic and polycyclic olefins include those of the structural formulae: 
wherein R1, R2, R3, R4, R5, R6, R7, and R8 are identical or different and are selected from the group consisting of hydrogen, C6-C16 aryl moieties, and C1-C8 alkyl moieties, it being possible for identical radicals in the different formulae to have different meanings.
The catalyst composition for use herein is formed by activating a metallocene procatalyst with a suitable catalyst. The terms xe2x80x9cmetallocenexe2x80x9d and xe2x80x9cmetallocene procatalystxe2x80x9d as used herein shall be understood to refer to compounds possessing a transition metal M, at least one non-cyclopentadienyl-derived ligand X and zero or one heteroatom-containing ligand Y, the ligand being coordinated to M and corresponding in number to the valence thereof. Such compounds, cocatalysts useful for their activation to provide metallocene catalysts that may be employed for the polymerization of olefins to provide polyolefin homopolymers and copolymers, and/or polymerization processes employing one or more of the metallocene catalysts are described in, among others, U.S. Pat. Nos. 4,752,597; 4,892,851; 4,931,417; 4,931,517; 4,933,403; 5,001,205; 5,017,714; 5,026,798; 5,034,549; 5,036,034; 5,055,438; 5,064,802; 5,086,134; 5,087,677; 5,126,301; 5,126,303; 5,132,262; 5,132,380; 5,132,381; 5,145,819; 5,153,157; 5,155,080; 5,225,501; 5,227,478; 5,241,025; 5,243,002; 5,278,119; 5,278,265; 5,281,679; 5,296,434; 5,304,614; 5,308,817; 5,324,800; 5,328,969; 5,329,031; 5,330,948; 5,331,057; 5,349,032; 5,372,980; 5,374,753; 5,385,877; 5,391,629; 5,391,789; 5,399,636; 5,401,817; 5,406,013; 5,416,177; 5,416,178; 5,416,228; 5,427,991; 5,439,994; 5,441,920; 5,442,020; 5,449,651; 5,453,410; 5,455,365; 5,455,366; 5,459,117; 5,466,649; 5,470,811; 5,470,927; 5,477,895; 5,491,205; and, 5,491,207, the contents of which are incorporated by reference herein.
The metallocene procatalyst is preferably one or a mixture of metallocene compounds of the following general formula:
(Cp1R1m)R3(Cp2R2p)MXq
wherein:
Cp1 of ligand (Cp1R1m) and Cp2 of ligand (Cp2R2p) are the same or different cyclopentadienyl rings;
R1 and R2 are independently selected from the group consisting of hydrogen, hydrocarbyl, halocarbyl, heterocarbyl, hydrocarbyl-substituted organometalloid, and halocarbyl-substituted organometalloid moieties, wherein, in each case, the carbyl moiety contains up to about 20 carbon atoms;
m is 0 to 5;
p is 0 to 5;
two R1 and/or R2 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated therewith can be joined together to form a ring fused to the cyclopentadienyl ring, the fused ring containing from 4 to about 20 carbon atoms;
R3 is a bridging group bridging Cp1 and Cp2;
M is a transition metal having a valence of from 3 to 6;
each X is a non-cyclopentadienyl ligand and is independently selected from the group consisting of halogen, hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid, and halocarbyl-substituted organometalloid moieties, wherein, in each case, the carbyl moiety contains up to about 20 carbon atoms; and
q is equal to the valence of M minus 2.
Methods for preparing these and other useful metallocene procatalysts are known in the art and do not constitute a part of the present invention.
When employing the foregoing metallocene procatalyst, and where the cocatalyst is entirely an aluminoxane, the ligand (Cp1R1m) must be different from the ligand (Cp2R2p), and the bridging group R3 must contain at least two bulky groups. Of these bridged metallocenes, it is preferred that bridging group R3 possess the structure 
in which bulky groups R4 and R5 each, independently, is, or contains, a cyclohydrocarbyl group containing up to about 20, and preferably from 6 to about 12, carbon atoms and from 0 to 3 heteroatoms, such as oxygen, sulfur, tertiary nitrogen, boron or phosphorus and, in particular, is cycloalkyl, heterocycloalkyl, cycloalkenyl, heterocycloalkenyl, aryl, heteroaryl, alkaryl, alkylheteroaryl, aralkyl, heteroaralkyl, and the like.
Preferably, M is titanium, zirconium, or hafnium, q is 2, and each X is halogen.
Of this preferred group of bridged metallocenes, those in which ligand (Cp1Rm1) is substituted or unsubstituted cyclopentadienyl, ligand (Cp2Rp2) is indenyl or fluorenyl, M is zirconium, R4 and R5 each is substituted or unsubstituted phenyl, and each X ligand is chlorine are still more preferred.
Still other preferred bridged metallocenes (I) that can be used in the polymerization process of this invention include:
diphenylmethylene(indenyl)(fluorenyl)zirconium dichloride;
diphenylmethylene(cyclopentadienyl-9-fluorenyl)zirconium dichloride;
diphenylmethylene(3-methyl-cyclopentadienyl-9-fluorenyl)zirconium dichloride;
diphenylmethylene(3-ethyl-cyclopentadienyl-9-fluorenyl)zirconium dichloride;
diphenylmethylene(3-propyl-cyclopentadienyl-9-fluorenyl)zirconium dichloride;
diphenylmethylene(3-butyl-cyclopentadienyl-9-fluorenyl)zirconium dichloride;
diphenylmethylene(cyclopentadienyl-indenyl)zirconium dichloride;
diphenylmethylene(cyclopentadienyl)(4,5,6,7-tetrahydro-indenyl)zirconium dichloride;
diphenylmethylene(cyclopentadienyl)(2-methylindenyl) zirconium dichloride;
diphenylmethylene(cyclopentadienyl)(2-phenylindenyl) zirconium dichloride;
diphenylmethylene(2,4-dimethylcyclo-pentadienyl)(3xe2x80x2,5xe2x80x2-dimethylcyclopentadienyl)zirconium dichloride;
diphenylmethylene(2-methyl-4-tert-butylcyclo-pentadienyl) (3xe2x80x2-tert-butyl-5xe2x80x2-methylcyclopentadienyl)zirconium dichloride;
dixylylmethylene(2,3,5-trimethylcyclopentadienyl) (2xe2x80x2,4xe2x80x2,5xe2x80x2-trimethylcyclopentadienyl)zirconium dichloride;
dixylylmethylene(2,4-dimethylcyclopentadienyl)(3xe2x80x2,5xe2x80x2-dimethylcyclopentadienyl)zirconium dichloride;
dixylylmethylene(2-methyl-4-tert-butylcyclopentadienyl) (3xe2x80x2-tert-butyl-5-methylcyclopentadienyl)zirconium dichloride;
dixylylmethylene(cyclopentadienyl)(fluorenyl)zirconium dichloride;
di-o-tolylmethylene(cyclopentadienyl)(3,4-dimethyl-cyclopentadienyl)zirconium dichloride;
di-o-tolylmethylene(cyclopentadienyl)(3,4-dimethyl-cyclopentadienyl)zirconium dichloride;
di-o-tolylmethylene(cyclopentadienyl)(3,4-dimethylcyclopentadienyl)zirconium dichloride;
di-o-tolylmethylene(cyclopentadienyl)(indenyl)zirconium dichloride;
dibenzylmethylene(cyclopentadienyl)(tetramethylcyclopentadienyl)zirconium dichloride;
dibenzylmethylene(cyclopentadienyl)(indenyl)zirconium dichloride;
dibenzylmethylene(cyclopentadienyl)(fluorenyl)zirconium dichloride;
dicyclohexylmethylene(cyclopentadienyl)(indenyl)zirconium dichloride;
dicyclohexyl(cyclopentadienyl)(fluorenyl)zirconium dichloride;
dicyclohexylmethylene(2-methylcyclopentadienyl)(fluorenyl) zirconium dichloride;
diphenylsilyl(2,4-dimethylcyclopentadienyl)(3xe2x80x2,5xe2x80x2-dimethyl-cyclopentadienyl)zirconium dichloride;
diphenylsilyl(2,4-dimethylcyclopentadienyl)(3xe2x80x2,5xe2x80x2-dimethyl-cyclopentadienyl)zirconium dichloride;
diphenylsilyl(2,3,5-trimethylcyclopentadienyl)(2,4,5-trimethylcyclopentadienyl)zirconium dichloride;
tetraphenyldisilyl(cyclopentadienyl)(indenyl)zirconium dichloride;
tetraphenyldisilyl(3-methylcyclopentadienyl)(indenyl) zirconium dichloride;
tetraphenyldisilyl(cyclopentadienyl)(fluorenyl)zirconium dichloride;
di-o-tolylsilyl(cyclopentadienyl)(trimethylcyclopentadienyl) zirconium dichloride;
di-o-tolylsilyl(cyclopentadienyl)(tetramethylcyclopentadienyl)zirconium dichloride;
di-o-tolylsilyl(cyclopentadienyl)(3,4-diethylcyclopentadienyl)zirconium dichloride;
di-o-tolylsilyl(cyclopentadienyl)(triethylcyclopentadienyl) zirconium dichloride;
dibenzylsilyl(cyclopentadienyl)(fluorenyl)zirconium dichloride;
dibenzylsilyl(cyclopentadienyl)(2,7-di-t-butyl-fluorenyl)zirconium dichloride;
dicyclohexylsilyl(cyclopentadienyl)(fluorenyl)zirconium dichloride; and the like.
The cocatalyst, or activator, employed with the preferred bridged metallocene procatalysts of formula (I) can be any of the aluminoxanes known to activate metallocene procatalysts. For further details of the aluminoxane cocatalysts including such alkylaluminoxanes as MAO see, e.g., U.S. Pat. No. 5,229,478. In general, the bridged metallocene procatalyst can be present in the reactor in an amount, expressed in terms of its transition metal content, of from about 0.0001 to about 0.02, preferably from about 0.0002 to about 0.015 and more preferably from about 0.00025 to about 0.01, millimole/liter. Corresponding to these amounts of transition metal, the aluminoxane cocatalyst can be utilized in an amount of from about 0.01 to about 100, preferably from about 0.02 to about 75 and more preferably from about 0.025 to about 50, millimoles/liter. It will, of course, be recognized that optimum levels of bridged metallocene procatalyst and aluminoxane cocatalyst will to some extent depend upon the specific procatalyst and cocatalyst selected, as well as other polymerization process variables.
When employing an aluminoxane cocatalyst, it can be advantageous to include a trialkylaluminum, such as trimethylaluminum, triethylaluminum, tri(n-propyl)aluminum, triisopropyaluminum, tri(n-butyl)aluminum, triisobutyl-aluminum, and the like, to reduce the amount of aluminoxane required for suitable activation of the metallocene procatalyst. In general, the optional trialkylaluminum can be utilized in a molar ratio to metallocene procatalyst of from about 1 to about 1000, preferably from about 2 to about 500.
It is also contemplated that a neutral or anionic metal- and/or metalloid-containing component can optionally be employed with the aluminoxane cocatalyst in activating the metallocene procatalyst.
Useful neutral metal- and/or metalloid-containing components for use herein include boranes such as perfluoroarylborane compounds, e.g., tris(pentafluorophenyl)borane, tris(methoxyphenyl)borane, tris(trifluoromethylphenyl)borane, tris(3,5-di[trifluoro-methyl]phenyl)borane, tris(tetrafluoroxylyl)borane, tris(tetrafluoro-o-tolyl)borane, etc., and the like. Of the foregoing boranes, tris(pentafluorophenyl)borane and tris(3,5-di[trifluoromethyl]phenyl)borane are preferred. Other useful second components include aluminum homologues of the foregoing compounds.
Suitable anionic metal- and/or metalloid-containing components for use herein include borates such as perfluoroaryl borates, e.g., lithium tetrakis(pentafluorophenyl)borate, lithium tetrakis(trifluoromethylphenyl)borate, lithium tetrakis(3,5-di{tri-fluoromethyl}phenyl)borate, sodium tetrakis(pentafluoro-phenyl)borate, potassium tetrakis(pentafluorophenyl)borate, magnesium tetrakis(pentafluorophenyl)borate, titanium tetrakis(pentafluorophenyl)borate, tin tetrakis(pentafluorophenyl)borate, dimethylanilinium tetrakis(pentafluorophenyl)borate, etc., and the like. Of the foregoing borates, dimethylanilinium tetrakis(pentafluorophenyl)borate and alkali metal borates, such as lithium tetrakis(pentafluorophenyl)borate and lithium tetrakis(3,5-di{trifluoro-methyl}phenyl)borate are preferred. Other useful components include aluminate homologues of the foregoing compounds.
In general, the optional neutral or anionic metal- and/or metalloid-containing components can be utilized in a molar ratio to metallocene procatalyst of from about 0.1 to about 10, preferably from about 0.5 to about 3.
Activation of the metallocene can be achieved by combining the aforementioned metallocene procatalysts with the aluminoxane cocatalyst either simultaneously or in any sequence and with any interval of time therebetween and either in the presence or absence of the olefin monomers and hydrogen.
It is particularly advantageous to prepare the activated metallocene catalyst composition in advance and thereafter introduce it into the polymerization reactor with the olefin monomers in the presence of hydrogen. The reaction of the metallocene procatalyst with the aluminoxane cocatalyst is advantageously conducted at a temperature ranging from about 0 to about 50xc2x0 C. for a time period of from about one minute to about 72 hours.
Copolymerization of the aforementioned monomers using hydrogen and the catalyst can be carried out in any known manner, e.g., in the liquid phase, i.e., in a solution or slurry process, or in a suspension process, either continuously or in batch. These processes are generally carried out at temperatures in the range of from about 0xc2x0 C. to about 200xc2x0 C., preferably from about 50xc2x0 C. to about 150xc2x0 C., and pressures from about 10 to about 3000 psig. As one skilled in the art would readily appreciate, control of the polymerization temperature has a direct bearing on the quality of the polymerization, e.g., activity, as well as the final product properties, e.g., Iodine Number. However, as these temperatures approach 150xc2x0 C. or greater, the exothermic temperature, i.e., the maximum temperature reached during the polymerization, should be substantially close to the initial polymerization temperature, e.g., at temperatures above about 150xc2x0 C. the exothermic temperature should be no more than about 20xc2x0 C. greater than the initial polymerization temperature.
The polymerization can be carried out in liquid monomer and in the absence of solvent or, if desired, in the presence of solvent. Dilution solvents that can be employed include straight and branched chain hydrocarbons, such as the butanes, the pentanes, the hexanes, the heptanes, the octanes, and the like, cyclic and alicyclic hydrocarbons, such as cyclopentane, cyclohexane, cycloheptane, methyl-cyclopentane, methylcyclohexane, methylcycloheptane, and the like, and alkyl-substituted aromatic compounds, such as toluene, xylene, and the like, and mixtures of the foregoing.
A typical batch solution polymerization process can be carried out by first introducing the xcex1-olefin, e.g., 1-decene, either alone or in combination with an optional hydrocarbon solvent, e.g., hexanes, xylenes, etc., into a stirred tank reactor. The bulky olefin, e.g., norbornene, can be added either sequentially or simultaneously with the xcex1-olefin. A minor amount of an inert impurity scavenger, e.g., the aforementioned trialkylaluminum compounds, can also be added at this time. The reactor is then brought up to the desired temperature, e.g., from about 0 to about 200xc2x0 C., preferably from about 20 to about 175xc2x0 C., and a measured amount of hydrogen can then be introduced into the stirred tank reactor. If copolymerization is desired with a gaseous monomer, a monomer feed comprising, for example, ethylene or 1-propene, is then sparged into the liquid phase, either in combination with, or separate from the hydrogen feed. By carrying out the polymerization reaction in the presence of hydrogen and employing the catalyst herein, a hydrogenation step is eliminated and the liquid poly(xcex1-olefins) of this invention are substantially saturated and, therefore, will possess a low iodine value, e.g., an Iodine Number of from about 0.0 to about 10, preferably from about 0.1 to about 5, and most preferably from about 0.2 to about 3.
Once the desired conditions are established, a hydrocarbon solution of the catalyst in the required amount is then added to the liquid phase in the reactor. The rate of polymerization is controlled by the concentration of the catalyst and monomers present or added during polymerization. The reactor temperature is controlled by means of cooling coils, etc., and the initial total pressure in the reactor is maintained by a constant flow of hydrogen, inert gas, gaseous monomers or a combination thereof. After polymerization is complete, the reactor is depressurized and the catalyst is deactivated by conventional means.
Depending on the amount of monomer conversion and viscosity of the reactor contents, a hydrocarbon solvent can be added to aid in removal the product polyolefin. Spent catalyst components can be isolated from the reaction product via mixing with, e.g., alcohol, water, or a mixture of both, then by phase separation of the hydrocarbyl component from the aqueous component. The liquid polyolefin can then be recovered from the hydrocarbyl component by conventional methods, e.g., evaporation, distillation, etc., and then further processed as desired.
The poly(xcex1-olefin) copolymers that can be obtained by the polymerization process herein are substantially amorphous, i.e., a crystalline phase is substantially absent from the resulting polyolefin as defined by an exothermic peak observation in a differential scanning calorimetry (DSC) experiment. In addition to being substantially amorphous, the poly(xcex1-olefin) copolymers that can be obtained by the polymerization process herein possess a unique combination of low weight average molecular weight (Mw), low polydispersity index (Mw/Mn, where Mn is number average molecular weight), controllable kinematic viscosity (Kv100), high viscosity index (VI), low Iodine Number (I2#), i.e., a substantially saturated polyolefin, and low glass transition temperature (Tg) that distinguish them from known polyolefins. The novel poly(xcex1-olefin) copolymers possess a Mw of from about 500 to about 80,000, preferably from about 750 to about 60,000 and more preferably from about 1,000 to about 40,000, a Mw/Mn of from about 1.0 to about 10, preferably from about 1.5 to about 5, more preferably from about 1.75 to about 4, a Kv100 of from about 10 to about 10,000, preferably from about 20 to about 7,500, more preferably from about 25 to about 5,000, an Iodine Number of from about 0.0 to about 10, preferably from about 0.1 to about 5, more preferably from about 0.2 to about 3, and a Tg of below about xe2x88x9220xc2x0 C., preferably below about xe2x88x9230xc2x0 C., more preferably below about xe2x88x9240xc2x0 C.
These advantageous properties can be exploited in a variety of products such as, for example, products which require a viscous oil or an inert material with fluid properties such as dispersants, heat transfer fluids, cosmetics, or other such consumer products, and the like. Additionally, the products of this invention can be used in grafting applications to produce functionalized low molecular weight polymers. The poly(xcex1-olefin) polymers of this invention are particularly useful as viscosity modifiers for lubricants, especially lubricating oils, wherein the polymer is employed in a viscosity-modifying amount. Concentrations of from about 1 to about 99 weight percent based on the total weight of the lubricant composition can be used. Preferably, the concentration is from about 5 to about 85 weight percent.
In general, mineral oils, both paraffinic, naphthenic and mixtures thereof, including those oils defined as American Petroleum Institute Groups I, II, and III can be employed as the lubricant vehicle, and can be any suitable lubricating viscosity range, as, for example, from about 2 cSt at 100xc2x0 C. to about 1,000 cSt at 100xc2x0 C., preferably from about 2 to about 100 cSt at 100xc2x0 C. These oils can have viscosity indices preferably ranging to about 180. The average molecular weights of these oils can range from about 250 to about 800.
Where synthetic oils are employed, they can include, but are not limited to, polyisobutylene, polybutenes, hydrogenated polydecenes, polypropylene glycol, polyethylene glycol, trimethylpropane esters, neopentyl and pentaerythritol esters, di(2-ethylhexyl) sebacate, di(2-ethylhexyl) adipate, dibutyl phthalate, fluorocarbons, silicate esters, silanes, esters of phosphorus-containing acids, liquid ureas, ferrocene derivatives, hydrogenated synthetic oils, chain-type polyphenyls, siloxanes and silicones (polysiloxanes), alkylsubstituted diphenyl ethers typified by a butyl-substituted bis(p-phenoxy phenyl) ether, and phenoxy phenylethers.
The lubricant compositions can also contain one or more other materials, for example, detergents, corrosion inhibitors, oxidative inhibitors, dispersants, pour point dispersants, anti-foaming agents, anti-wear agents, other viscosity modifiers, friction modifiers, and the like at the usual levels in accordance with well known practice. Other materials, including extreme pressure agents, low temperature properties modifiers, and the like, can also be used, as exemplified, respectively, by metallic phenates or sulfonates, polymeric succinimides, non-metallic or metallic phosphorodithioates, and the like, at the usual levels in accordance with well known practice. These materials do not detract from the value of the compositions of this invention, but rather serve to impart their customary properties to the particular compositions in which they are incorporated.
Various features and aspects of the present invention are illustrated further in the examples that follow. While these examples are presented to show one skilled in the art how to operate within the scope of the invention, they are not intended in any way to serve as a limitation upon the scope of the invention.